chore: replace GCP streams with iter.Seq2

[lionello]

Description

Applying the existing iter.Seq2 pattern to GCP logging.

Linked Issues

Checklist

• I have performed a self-review of my code
• I have added appropriate tests
• I have updated the Defang CLI docs and/or README to reflect my changes, if necessary

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
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